x11-session-research/worklist.md

Work items — x11-session-research

Governing rule (every phase)

Campaign-contained data acquisition. Every measurement this campaign relies on is acquired in this campaign's session. Predecessor numbers are reference history, never imported as binding cells, comparison targets, or success thresholds. The A1 baseline below is not optional — it is the in-session Wayland anchor against which X11 cells are compared. See phase0_findings.md § "Campaign-contained data discipline" and README.md § "Campaign-contained data discipline" for the full rule and the predecessor lesson that motivated it.

Phase 0 — substrate + research question + inventory

Status: IN PROGRESS. Motivation LOCKED 2026-05-03 in phase0_findings.md § "Research question". Pre-Phase-1 inventory and baseline-anchor work below.

• Predecessor close-out summarised. Substrate doc lists what transfers from kwin_overlay_subsurface and what's Wayland-specific (KWin source-reads don't transfer to X11 path).
• Research question locked. "Does cutting out the KWin compositor enable faster video display of Brave, chromium-fourier, and Firefox — for full SW decoding, and for libva decoding (where possible) — on PineTab2 RK3568?"
• Mechanism captured. Operator-supplied insight 2026-05-03: hantro emits NV12, rockchip-drm overlay plane doesn't accept NV12, so KWin must own the only NV12-capable plane (Primary, Plane 39) and forces GL-composite of every NV12 buffer. X11 + non-compositing WM can give the video region directly to Plane 39 and put rest of desktop on Plane 45 (RGB AFBC) — hardware-blended, no GL-composite.
• Experimental matrix drafted. 3 browsers × 2 decode paths × 2 sessions = 12 cells (some N/A where libva isn't supported). See phase0_findings.md § "Experimental matrix".
• State snapshot of ohm under current Plasma Wayland — the campaign-start before photo. Unattended-tractable via SSH. Captures package versions, kernel, kwin_wayland PID + cmdline, governor, services, browser binary versions, test asset paths, thermal_zone temps.
• Inventory of available X11 paths on ohm. Captured 2026-05-03 in phase0_evidence/x11_inventory_2026-05-03/ (raw 02_x11_paths.txt + summary inventory.md § "Deliverable 2"). Verdict: xorg-server 21.1.22 + Mesa 26.0.5 / Panfrost healthy, modesetting (in-server) is sole DDX, only kwin_x11 WM installed today, six WM candidates available in extra, Plasma X11 + Plasma Wayland + Weston are the SDDM-advertised sessions. Operator action: pacman -S a non-compositing WM (recommend openbox) and create/switch to its SDDM session before without-KWin cells can run.
• NEW: Browser X11-overlay-path inventory. Per phase0_findings.md § "Open questions": determine whether Brave 147 ozone-x11, chromium-fourier 149 ozone-x11, and Firefox X11 backends actually request hardware-overlay presentation for windowed video, or whether they always internally composite to RGB. Browser-specific source-grep
  • chrome trace inspection.
• NEW: Add mpv as a reference X11-overlay client. mpv with --vo=xv or --vo=gpu --gpu-context=x11 is a known-good X11 hardware-overlay path. Adding mpv to the matrix as a 4th client provides "is the X11 hardware-overlay path even reachable on this hardware" baseline, separate from "do browsers use it." If mpv hits Plane 39 NV12 cleanly but browsers don't, the answer is "X11 path is fast, but the browsers don't take advantage of it."
• Inventory of X11-side measurement instruments. Captured 2026-05-03 in phase0_evidence/x11_inventory_2026-05-03/ (raw 04_measurement_instruments.txt + summary inventory.md § "Deliverable 4"). Live X server supports all 7 needed extensions (Composite, DAMAGE, DRI3, Present, RANDR, SYNC, XVideo). Tools installed: xprop, xdpyinfo, xset, glxinfo, drm_info, perf, mpv, libxcb-present. Tools missing-but-in-extra: xrandr CLI, xev, xinput, xwininfo, xkill, sysprof — one pacman -S away. AUR-only: X-protocol xtrace (the /usr/bin/xtrace from glibc is a syscall tracer, unrelated); optional, matrix doesn't strictly need protocol traces. perf_event_paranoid=2 — set to 1 once for unattended runs.
• A1 baseline: in-session Wayland-with-KWin anchor. Mandatory per the governing rule. 3 reps minimum (variance is a real concern on this hardware per the predecessor data) of a kwin_timing_nodebug-equivalent run on the current Plasma Wayland session, captured into phase0_evidence/wayland_baseline_repN/. This is the only Wayland baseline this campaign uses. No predecessor number substitutes for these reps even if the predecessor measured an "identical" condition. The 3 reps also surface the session-internal variance up front, so Phase 1 thresholds aren't drawn against a single sample.

Phase 1 — binding cells + measurement protocol

Pending Phase 0 inventory + A1 baseline anchor. Phase 1 lock will produce phase1_lock.md with:

• Binding cells per matrix cell (effective_fps, drops_total, drops_post_warmup, end-to-end-latency-if-testable, compositor+browser CPU at steady state).
• The clear-pass / clear-fail thresholds: what "X11 is faster" means quantitatively. Thresholds are drawn from the A1 Wayland baseline acquired in this campaign — not from predecessor numbers. Provisional shape (numbers TBD from A1): a matrix cell counts as "X11 faster" if its effective fps exceeds the campaign's same-cell Wayland median by a margin larger than the campaign's same-cell Wayland IQR, and its drops_post_warmup is materially below the same cell's Wayland median.
• The measurement protocol per matrix cell, including how the X11 sessions are entered and how the browser is launched with libva forced on/off. Mirrors the structure of kwin_overlay_subsurface/phase3_protocol.md.

Phase 2-onwards

Pending.

Discipline carry-overs from kwin_overlay_subsurface

• Campaign-contained data acquisition — see governing rule at the top of this file. The strongest version of the predecessor's "replicate the baseline first" lesson: don't import predecessor data at all, acquire it fresh.
• Phase discipline — no patches before source-read is documented. Re-scoping must be honest about deferral target.
• Non-upstreaming default — bug reports + MRs are explicit operator-tasked decisions.
• Memory persistence rule — when this campaign reaches its diagnostic terminal state (success or honest closure), update project_campaign_overview.md and add any new feedback memory worth carrying forward to the next campaign.